The present invention relates to an automatic analyzer that automatically makes qualitative/quantitative analyses of blood, urine, and other biological samples, and more particularly to an automatic analyzer that incorporates a function for dispensing a liquid from one vessel to another with a pipette probe.
The automatic analyzer dispenses a blood, urine, or other biological sample from its vessel into a reaction vessel, then dispenses a reagent from its vessel into the reaction vessel, which contains the dispensed biological sample, and measures color changes in a mixture of the sample and reagent with a photometer or other measuring means.
When the sample and reagent are to be dispensed, the end of a pipette probe is dipped in the liquid to be dispensed. The greater the dipping depth, the larger the amount of liquid deposited on the outer wall of the probe and thus the greater the degree of contamination between different samples and reagents. A method generally employed for minimizing the pipette probe dipping depth is to stop the descent of the probe when its end is positioned slightly below the liquid surface after the surface of the contained liquid is detected, and then exercise operational control so as to suction a specified amount of liquid for transfer to the probe. In this instance, a technology for accurate liquid surface detection is essential. Various technologies have been proposed to achieve the above purpose, including a method for measuring changes in the capacitance between a pipette probe and liquid and a method for measuring changes in the pressure within a pipette probe.
While a sample or reagent is being dispensed, the surrounding air may be taken in so as to bubble on the liquid surface. In such an instance, a capacitance measurement method (which makes use of a significant capacitance change that occurs when a pipette probe comes into contact with a liquid) may erroneously conclude that the liquid surface is reached when the pipette probe comes into contact with the bubble surface, thereby making it impossible to dispense a specified amount of reagent or sample. The automatic analyzer disclosed by Japanese Patent Laid-Open No. Hei 148207 incorporates a function for turning off a liquid surface detection circuit so as not to erroneously recognize a bubble as the liquid surface and includes means for calculating the pipette probe descent position necessary for minimizing the contact between a reagent or other liquid in a reaction tube and the pipette probe for sample dispensing in accordance with the amount of reagent or other liquid discharged beforehand into the reaction tube, and stopping the descent of the pipette probe in compliance with the calculated value.
Some reagents contain constituents that readily deposit as well as a surface-active agent that is likely to bubble. To obtain consistent analysis results from the use of one of such reagents, it is necessary to periodically stir it during the analyzer's analysis operation for the purpose of making the reagent concentration uniform within a reagent vessel. Therefore, the reagent surface bubbles after such a stirring operation. After the stirring operation is repeated a certain number of times, a layer of bubbles may be formed on the reagent liquid surface.
As a result, when an attempt is made to detect the reagent liquid surface within the reagent vessel, the layer of bubbles may be erroneously detected instead of the true reagent liquid surface so as to start a dispensing operation before the end of the probe reaches the liquid surface. In other words, reagent bubbles may be dispensed instead of the reagent liquid so that an inadequate amount of reagent is dispensed. Eventually, an analysis result error may occur.
The technology disclosed by Patent Document 1 above uses the amount of a reagent or other liquid discharged into a reaction tube to calculate the surface of the reagent or other liquid in the reaction tube. However, this technology cannot calculate the reagent liquid surface if the surface of a reagent liquid initially contained in a reagent vessel is bubbled.